Limiting Reagent/Reactan Worksheet - Report of Fundamental Chemistry - IPSE FPMIPA Universitas Pendidikan Indonesia

 Limiting Reagent/Reactant

Basic Theory 

In many reactions, one reactant becomes entirely consumed and the other reactant is left over. The reactant that becomes consumed is called the limiting reagent. When the limiting reagent is all consumed, no more product can be formed (reaction complete). The reactant limits the amount of product that can be formed. In the sandwich analogy above the bread, cheese and ham are not just analogies for the reactants; they also represent the number of moles or particles available for reaction. As soon as one reactant is consumed, the reaction stops because there are no longer particles of that reactant available for reaction. The reaction is limited by the availability of this reagent. In this experiment, you will predict and observe a limiting reactant during the copper (II) chloride oxidation. You will use the single displacement reaction of aluminum with aqueous copper (II) chloride. 2Al(s) + 3CuCl2(aq) → 3Cu(s) + 2AlCl3(aq) Copper (II) chloride, CuCl2, turns a light blue in aqueous solution. This is due to the Cu2+(aq) ion. Aluminum chloride is colourless in aqueous solution. Copper is mankind’s oldest metals, dating back more than 10,000 years. The copper (II) chloride oxidation reaction has been used in petroleum industries for sweetening (a refining process used to remove sulfurous gases from natural gas). This process has also been used for etch regeneration, in which CuCl2 is used to remove unwanted copper from printed wiring boards and discrete areas are etched away.

Objectives 

In this experiment, you will be:
o predicting and observing the limiting and excess reagents in a reaction.
o distinguishing between different substances (reactants and products) based on their changes in                colouration.
o distinguishing between limiting and excess reagents in a reaction.
o conducting limiting reagent calculations.
Group’s Member: 1. 2 3. 4. 

Materials
▪ 100 ml beakers (3)
▪ Stirring rod (2)
▪ Analytical Balance
▪ 0.81 g & 0.4 g Copper chloride
▪ 0.27 g Aluminum foil
▪ Distilled water
▪ Watch Glass
▪ Spatula
▪ 100 ml graduated cylinder (1)

Safety

o Place the beakers flat on a surface as the reaction proceeds because it may become hot.
o Dispose of the substances in a waste container as directed by your teacher

Procedures 

1. Using a balance, weigh 0.81 g CuCl2 and 0.27 g Aluminum foil. 

2. Place the Al and CuCl2 into the first 100 ml beaker. 

3. Using a balance weigh out a further 0.4 g of copper chloride (1/5 as much) and the same amount             (0.27 g) of aluminum. 

4. Again, place the Al and CuCl2 into another 100 ml beaker. 

5. Look at the contents of each beaker. When water is added to the beakers, the CuCl2 will dissolve and     the reaction will proceed. By looking at the amount of reactants in each container, in which one do         you think that there is excess reactant? In which container do you think there is a limiting reagent? 

6. Using a graduated cylinder, measure 50 ml of distilled water and add to each beaker. 

7. Record the colour of substances and any other observations (smell, bubbling, heat formation, etc.)         that are visible at the beginning of the reaction in the data table. 

8. Stir the substances in the beakers occasionally with the stirring rod. 

9. Record any colour changes or any other observations as the reaction proceeds in the data table. 

10. Record the colour of all substances and any other observations at the end of the reaction in the data       table. 

11. When the reaction is complete, return the beakers, with its contents, to your teacher for proper               disposal.

Observation Table 

Record information below. Ensure to make note of any differences in the reactions. Observations (Colour, Bubbles, Heat, Smell, etc.) Beginning of reaction During the reaction End of reaction

Data Analysis 

1. In this experiment, what does the colour change represent? Explain your answer in terms of changes from atoms to ions and ions to atoms. You may wish to illustrate the chemical change occurring at the molecular level. 

2. According to your observations, which reactant was present for the longest period of time in the first reaction with 0.81 g CuCl2? Is this the limiting or excess reagent? Explain. 

3. According to your observations, which reactant was present for the longest period of time in the second reaction with 0.4 g CuCl2? Is this the limiting or excess reagent? Explain. 

4. According to your observations, which reactant was present for the shortest period of time in the first reaction with 0.81 g CuCl2?? Is this the limiting or excess reagent? Explain.

5. According to your observations, which reactant was present for the shortest period of time in the first reaction with 0.4 g CuCl2? Is this the limiting or excess reagent? Explain.

6. Are limiting reagents present in all reactions. Explain? 

7. In these experiments, when and why did the reaction stop? Explain your answer at the particle level in regards to reactants available.

8. Draw a diagrammatic representation for the balanced equation shown below, using the following symbols to represent the particles involve at the molecular level involved in the reaction. Are there any limiting or excess reagents? Why or why not?

Symbols
Al Cu Cl
Before Reaction After Reaction
2Al(s) + 3CuCl2(aq) → 3Cu(s) + 2AlCl3(aq) 

9. Can we tell from just the masses which of the two reactants will potentially be the limiting reagent? Why or why not? Keep in mind what is happening at the molecular level in a chemical reaction. 

10. The mass allows us to determine the number of moles and thus the number of particles
available to react. Answer the following questions, using your observations and the equation below from your investigation: __Al(s) + __CuCl2(aq) → __Cu(s) + __AlCl3(aq) 

a) Balance the equation. 

b) Based on the lab data, calculate the number of moles of each reactant in just the first reaction, using their original masses (0.81 g CuCl2 and 0.27 g Aluminum
 foil). Set these calculations up in a way logical to you to calculate. Otherwise, use the formula below: 1 mol CuCl2 = ? g 1 mol Al = ? g ? mol = 0.81 g ? mol = 0.27 g 

c) Using the balanced equation, calculate the number of moles of Aluminum needed to react with all the copper (II) chloride present. 

d) Which reactant is the limiting reagent? Compare the moles of Al calculated in part b to the moles of Al calculated in part c. 

e) Which reactant is the excess reagent? 

f) What is the maximum number of moles of AlCl3 that can be produced, based on the moles of limiting reagent (LR) present in the reaction? 

g) What is the maximum number of grams of AlCl3 that can be produced?

Conclusion

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